A gas turbine engine may be used to power aircraft or various other types of vehicles and systems. The engine typically includes a compressor that receives and compresses an incoming gas such as air; a combustion chamber in which the compressed gas is mixed with fuel and burned to produce exhaust gas; and one or more turbines that extract energy from the high-pressure, high-velocity exhaust gas exiting the combustion chamber.
In the manufacture of gas turbine engines, and in particular in engine development programs, the date at which the first engine can be tested is limited by the long schedule required to fabricate the cooled turbine parts such as blades and vanes. For example, cooled turbine airfoils are typically one of the “critical path” components in gas turbine engine fabrication, the completion of which is required prior to any engine testing. Due to the expensive tooling and fabrication costs for these components, limited quantities of hardware are purchased for development programs.
Recently, additive manufacturing methods have emerged, including for example the use of direct metal laser sintering/fusion (DMLS)/(DMLF), selective laser sintering (SLS), and electron beam melting (EBM), to eliminate the need for tooling, which is expected to result in significant cost and cycle time reduction in the manufacture of gas turbine engines. However, the high temperature, high strength nickel based super alloy materials currently employed in such additive manufacturing methods have a tendency to crack after build, rendering the component unusable for engine testing.
EBM uses an electron beam and DMLF uses a laser to solidify a metal powder. Parts are built in small layers (a few mils) in additive steps to produce a completed part. Fine powdered alloys are sintered and melted into a final part. The mechanics of the DMLF and EBM build processes are similar, except for the fact that the DMLF process uses a laser and the EBM process utilizes an electron beam. Both energy sources melt fine layers of powder and fuse that layer to the subsequent layer directly below it.
With both DMLF and EBM technologies, it is desirable to eliminate cracking during build and during post build processes. Using current DMLF technology, the process does not maintain acceptable thermal gradients in the part during build. The resulting thermal gradients induce thermal stresses that may produce cracking during build and post build processing. Similarly, EBM technology may produce a homogenous component, but there is a still a tendency for cracking.
Accordingly, it is desirable to provide improved additive manufacturing techniques that reduce the tendency of the completed part to crack post-build. Further, it is desirable to provide components for use in gas turbine engines quickly and efficiently such that the design-to-test time for the gas turbine engine is reduced. Furthermore, other desirable features and characteristics of the invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.